An image stabilizing instrument exhibits a stable image even if its housing is subject to unwanted movements. This is made possible when an internal cardan pivoted, inertially stabilized part is carrying optics that are designed so as to define the line of sight of the instrument. This concept is common to essentially all efficient image stabilizing instruments. However, the kind of optics subject to cardan suspension varies greatly. Numerous concepts have been proposed, mostly referring to monocular instruments. The potential user, though, has favored binocular instruments and considerable efforts have been exercised to finding such solutions, even if the progress has been limited.
Concepts of monocular image stabilization may be employed in binocular instruments if the optics in the two binocular halves are linked together with bridges between additional pivot axes, as exemplified in U.S. Pat. No. 2,829,557. This, however, means a considerable mechanical complexity and, to the knowledge of this inventor, no such instrument has ever been produced. For this reason, concepts have been developed where only one cardan pivoted mechanical part is stabilizing the two optical parts of a binocular system. However, this has proved to lead to surprisingly great problems.
In U.S. Pat. No. 4,235,506, an image stabilized binocular is shown where only one part is cardan pivoted. A drawback here is that the objectives are non-stabilized which leads to a small aperture, considerable aberrations during panning or heavy, complicated objectives. Another great disadvantage is that the two image erecting prisms are joined together in a stabilized part, which leads to a double image at horizontal panning. The stereo characteristics are also inferior. In spite of these shortcomings this seems to be the most commonly used concept today, which should illustrate the difficulty of the problem.
U.S. Pat. No. 4,542,962 suggests a binocular without the above drawbacks. Unfortunately there are others instead: The image is tilted when the binocular is moved in the vertical plane, which may be seen as a drawback by the user. Special so-called roof mirrors--two precisely aligned plane mirrors--are employed for the maybe most interesting design (see FIG. 11). Complicated mechanics is required for the variable inter-ocular distance. It is hard to find space in the light path for Barlow lenses without adversely increasing the size of the binocular. The system also exhibits other drawbacks.
No possible variation according to U.S. Pat. No. 4,542,962 takes care of all these problems. One finds that good characteristics may be achieved in the vertical plane, this, however, excludes good characteristics in the horizontal plane. Likewise other variations may give good characteristics in the horizontal plane but not in the vertical plane.
The magnification in image stabilized binoculars may be substantially increased over the values for the non-stabilized ones thanks to the fact that the unwanted movements of the housing does not give rise to problems. However, naturally the field of sight and the light power decreases when the magnification increases. Therefore the possibility to switch between at least two magnifications would be of great advantage. Common to all embodiments mentioned above is that this hardly may be implemented in an efficient way.
Swedish Patent 503,932, issued Sep. 30, 1996, discusses an image stabilizing instrument having two objectives (2) and two reflecting optical elements (3) attached to a stabilized frame (22), uni-axially pivoted in a cardanic part (11). Second optical elements (4) are fastened to the cardanic part (11), which in turn is uni-axially pivoted in the binocular housing (9). The entire contents of this Swedish Patent is incorporated herein by reference.
This Swedish patent does not take into consideration and correct for color aberration.